#include "apue.h"
#include <errno.h>
#include <fcntl.h>
#include <sys/wait.h>


static pid_t *childpid = NULL;

static int maxfd;

FILE *
popen(const char *cmdstring, const char *type) {
	int i;
	int pfd[2];
	pid_t pid;
	FILE *fp;

	if ((type[0] != 'r' && type[1] != 'w') || type[1] != 0) {
		errno = EINVAL;
		return (NULL);
	}

	if (childpid == NULL) {
		maxfd = open_max();	

		if ((childpid = calloc(maxfd, sizeof(pid_t))) == NULL) {
			return (NULL);
		}
	}

	if (pipe(pfd) < 0) {
		return (NULL);
	}
	if (pfd[0] >= maxfd || pfd[1] >= maxfd) {
		close(pfd[0]);
		close(pfd[1]);
		errno = EMFILE;
		return (NULL);
	}

	if ((pid = fork()) < 0) {
		return (NULL);
	} else if (pid == 0) {
		if (*type == 'r') {
			close(pfd[0]);
			if (pfd[1] != STDOUT_FILENO) {
				dup2(pfd[1], STDOUT_FILENO);
				close(pfd[1]);
			}
		} else {
			close(pfd[1]);
			if (pfd[0] != STDIN_FILENO) {
				dup2(pfd[0], STDIN_FILENO);
				close(pfd[0]);
			}
		}

		for (i = 0; i < maxfd; i++) {
			if (childpid[i] > 0) {
				close(i);
			}
		}

		execl("/bin/sh", "sh", "-c", cmdstring, (char *)0);
		_exit(127);
	}

	if (*type == 'r') {
		close(pfd[1]);
		if ((fp = fdopen(pfd[0], type)) == NULL) {
			return (NULL);
		}
	} else {
		close(pfd[1]);
		if ((fp = fdopen(pfd[1], type)) == NULL) {
			return (NULL);
		}
	}

	childpid[fileno(fp)] = pid;
	return (fp);
}


int 
pclose(FILE *fp) {
	int fd, stat;
	pid_t pid;

	if (childpid == NULL) {
		errno = EINVAL;
		return (-1);
	}

	fd = fileno(fp);
	if (fd >= maxfd) {
		errno = EINVAL;
		return (-1);
	}

	if ((pid = childpid[fd]) == 0) {
		errno = EINVAL;
		return (-1);
	}

	childpid[fd] = 0;
	if (fclose(fp) == EOF) {
		return (-1);
	}

	while (waitpid(pid, &stat, 0) < 0) {
		if (errno != EINTR) {
			return (-1);
		}
	}

	return (stat);
}

int 
main(void) {
	char line[MAXLINE];
	FILE *fpin;

	if ((fpin = popen("ch15_tolower", "r")) == NULL) {
		err_sys("popen error");
	}

	for (;;) {
		fputs("prompt > ", stdout);
		fflush(stdout);
		if (fgets(line, MAXLINE, fpin) == NULL) {
			break;
		}
		if (fputs(line, stdout) == EOF) {
			err_sys("fputs error to pipe");
		}
	}
	if (pclose(fpin) == -1) {
		err_sys("pclose error");
	}

	putchar('\n');
	exit(0);
}
